1. Field of the Invention
This invention pertains, in general, to medical devices, and in particular, to a tandem syringe for the gravity-feed, intravenous administration of parenteral liquids, such as medications and the like, and the method of its use.
2. Description of the Related Art
The intravenous ("I.V.") administration of drugs has increased dramatically over the past decade and approximately 40% of all drugs and fluids delivered to patients in hospitals today are administered intravenously..sup.1 FNT .sup.1. M. J. Akers, et al., "Intravenous Drug Delivery Primer," American Journal of Hospital Pharmacy, Vol. 44, p.2528, et seq., Nov. 1987.
Over the years, a wide variety of devices and methods have been developed to assist the health care practitioner in the I.V. delivery of fluids and medicaments. These systems may be broadly catagorized into those which accomplish their function immediately or contemporaneously, and those which achieve delivery intermittently or continuously over an extended period of time. They may be further grouped between those which achieve delivery by means of a "push," or positively-applied force acting on the fluid, and those which are gravity-feed.
An example of device which can accomplish I.V. delivery either immediately or intermittantly by means of a "push" is the well-known hypodermic syringe, which comprises a hollow barrel having a with a needle on it and a sliding piston plunger within. Typically, the syringe is used both to withdraw the liquid medication from a supply vial and to inject it subcutaneously and/or intravenously through the agency of the same needle by means of an immediate "push" supplied manually by the health practitioner, or intermittently or continuously over a period of time by the use of an associated battery- or spring-operated syringe pump.
Examples of "tandem" syringes having specialized functions, such as the push delivery of dual dosages of drugs, may be found in patents to J. L. Pizzino (U.S. Pat. No. 4,702,737), S. J. Ashley (U.S. Pat. No. 4,313,440), and J. A. Lazarte, et al. (U.S. Pat. No. 2,939,459). E. A. Tischlinger, in U.S. Pat. No. 4,059,109, and W. A. Gettig, in U.S. Pat. No. 4,581,016, each describe another type of syringe capable of mixing a diluent with a dry medication prior to its injection. In U.S. Pat. No. 4,685,910, R. J. Schweizer describes a type of syringe capable of delivering secondary fluids within a primary I.V. administration set utilizing a peristaltic infusion pump.
An example of apparatus typically utilized for gravity-feed of parenteral fluids is found in a patent to R. C. Moore, U.S. Pat. No. 2,866,457. Such systems typically comprise a relatively large container, usually a flexible plastic bag, of a primary parenteral fluid which is suspended above the patient to generate a pressure head greater than the the vasopressure of the patient, along with a length of flexible tubing terminating in an indwelling venocatheter. Intermediate the container and the catheter are typically found a check valve, a flow-control/shutoff clamp, and more proximal to the patient, a Y-connector which may be used to administer, either by push or gravity-feed, a secondary fluid in the "piggyback" fashion described below.
Gravity-feed I.V. delivery systems almost always are of the catagory which operate intermittantly or continuously over a period of time, as opposed to immediately. A detailed overview of various types of such intermittent I.V. systems, along with their attendent characteristics and problems, is provided by R. P. Rapp..sup.2 FNT .sup.2. R. P. Rapp, "Considering product features and costs in selecting a system for intermittent I.V. drug delivery," Am. J. Hosp. Pharm., Vol.44, pp.138l-91.
It is occasionally desirable to administer a small, secondary dose of medication intermittantly or continuously over an interval of time to a patient to whom a primary I.V. set is already connected. This is presently accomplished by "piggybacking" a "minibag" containing the medication onto the primary system and delivering it through the same venipuncture utilized by the primary system.
In such a procedure, the dose is typically withdrawn from the supply vial using a conventional disposable hypodermic syringe in the manner described above and then injected with that same syringe into a small, sterile, plastic "minibag". The dose may be diluted with a larger quantity of the primary parenteral fluid or other diluent in the same manner. The minibag of solution is then suspended above the container of the primary set and connected through a secondary I.V. set to an entry port on the primary set's Y-connector. The higher pressure head in the minibag causes a check valve in the primary set to close and shut off flow of the primary fluid, and secondary infusion is accomplished from the minibag by gravity-feed.
The minibags used in the above-described procedure are relatively expensive, and it would be more cost effective if the same disposable syringe which was used to measure and withdraw the medication from the supply vial could be used to gravity-feed the medication. A gravity-feed syringe system which is said to achieve this end is described by R. P. Rapp,.sup.3 and comprises a conventional disposable syringe which is suspended by means of plastic bag after it is filled and connected to the patient or primary set by means of a secondary set which includes a special vented fitting. FNT .sup.3. Id., at p. 2535.
Unfortunately, the special vent fittings used by this system are relatively expensive and are occasionally unreliable because they vent the syringe through the Luer-lock-type fitting at its bottom, and the medication can backflow through the vent by gravity and inadvertently shut off flow through the system.
It is therefore desirable to provide a gravity-feed I.V. delivery system in which the same device is capable both of withdrawing and measuring a small-to-medium dose of a liquid medication from a conventional supply vial, and reliably administering the dose to the patient through a conventional primary or secondary I.V. set, and which may be cost-effectively disposed of thereafter. These objects and others are achieved in the tandem syringe of the present invention.